View Full Version : Closed Spectrum 48k Mainboard Rev 5 or 6

24th February 2017, 21:21
I am after a working rev 5 or 6 Spectrum 48k Mainboard for the rubber key version, does anyone have a spare for sale?

24th February 2017, 23:46
Whats wrong with your original board matey ?

25th February 2017, 01:36
Whats wrong with your original board matey ?

Long story!! I have a revision 2 board at the moment that has issues with a device I use called the Spectra 128. It's an expansion devise that enables RGB out and has a rom socket on it, you can plug in a device called the ZXC4, this is a programmable ROM that has 4 mb storage.

Games crash and hang a lot using this device with my rev 2 and apparently it is to do with the clock line on the Spectrumís expansion bus, which Spectra uses to synchronise its picture output with that of the Spectrum. This signal is notoriously poor, it should have square pulses of amplitude 5V but on some Spectrums it can be extremely low (2V or less) and very noisy. The Z80 CPU can cope but if an interface is connected that also uses the clock line then the voltage can drop lower still and potentially below the voltage level where the Z80 can reliably detect it.

Sinclair published some fixes for this problem, but it is a BIG job, lots of components to change, I think that replacing it with a rev 5 or 6 that does not have this issue might be cheaper and easier in the long run.

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3rd April 2017, 21:29
Found elsewhere, closing thread :)